Let a day removed from a period stay removed

Taking one day out of a period the planner placed did nothing that
lasted: the period still asked for a full week, so the next sync put the
day straight back. The option was disabled rather than lying about it.

A removed day is now recorded as its own thing — no leave for this
parent, this child, this date — and the planner honours it on every
later sync. It is kept apart from the working-day overrides, which
answer a different question about the calendar rather than about the
plan.

The day belongs to the parent whose band was clicked, so removing one
parent's day leaves their partner's alone; where both parents were to be
off on one funding arrangement, the partner is simply funded on their
own instead. A removed day shortens what the period is asking for rather
than counting as a day the plan failed to find, so the advice about
closing a shortfall does not start arguing for a day nobody wants.

Nothing is removed without a way back: the toast undoes it, and the day
itself is marked in the calendar and offers to restore.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ei7gCZzdd751uZtPzb1Pep

backend/app/db/connection.py

@@ -180,6 +180,23 @@ CREATE TABLE IF NOT EXISTS day_override (
     FOREIGN KEY (workspace_id) REFERENCES workspace(id) ON DELETE CASCADE
 );
 
+-- "The planner may not place leave for THIS parent, for THIS child, on THIS
+-- date" — see app/entities/planned_day_exclusion.py for why this is its own
+-- table and not another day_override.
+CREATE TABLE IF NOT EXISTS planned_day_exclusion (
+    id TEXT PRIMARY KEY,
+    workspace_id TEXT NOT NULL,
+    child_id TEXT NOT NULL,
+    parent_personal_data_uuid TEXT NOT NULL,
+    date DATE NOT NULL,
+    created_at TIMESTAMP NOT NULL,
+    updated_at TIMESTAMP NOT NULL,
+    UNIQUE(workspace_id, child_id, parent_personal_data_uuid, date),
+    FOREIGN KEY (workspace_id) REFERENCES workspace(id) ON DELETE CASCADE,
+    FOREIGN KEY (child_id) REFERENCES child(id) ON DELETE CASCADE,
+    FOREIGN KEY (parent_personal_data_uuid) REFERENCES personal_data(uuid) ON DELETE CASCADE
+);
+
 CREATE TABLE IF NOT EXISTS tip_dismissal (
     id TEXT PRIMARY KEY,
     workspace_id TEXT NOT NULL,
@@ -225,6 +242,8 @@ CREATE INDEX IF NOT EXISTS idx_invitation_invited_by
     ON workspace_invitation (invited_by_user_id);
 CREATE INDEX IF NOT EXISTS idx_vacation_days_workspace
     ON vacation_days (workspace_id);
+CREATE INDEX IF NOT EXISTS idx_planned_day_exclusion_workspace
+    ON planned_day_exclusion (workspace_id);
 """